Sliding vane compressor



March 7, 1939'. e. KOLLBERG ET AL 2,150,122

SLIDING VANE COMPRESSOR Filed March 20, 1937 Patented Mar. 7, 1939UNITED STATES,

SLIDING VANE COMPRESSOR Gustaf L. Kollberg, Milwaukee, and Melvin 0-.

Shaw, Wauwatosa, Wis., assignors to Allis- Chalmers ManufacturingCompany, Milwaukee,

Wis., a corporation of Delaware Application March 20, 1937, Serial No.132,046

8 Claims.

This invention relates in general to improvements in compressors of thesliding vane type, and more particularly to an improved multistagecompressor having a unitary casing including therein the compressorcylinders and an interstage reservoir or intercooler.

Each cylinder of a. sliding vane compressor must be provided withso-called floating rings for supporting the rotor vanes and preventingrubbing thereof against the cylinder wall under the action ofcentrifugal force, as it is very difficult to avoid excessive and unevenwear of the cylinder when the vanes are allowed to apply themselvesdirectly'against the surface thereof. when floating rings are used,however, appreciable clearances must be provided between the rings andthe walls of the slot containing them, in order that the rings mayeasily be driven by the vanes of the rotor simply by frictionalengagement therebetween. Due to such clearances, leakage takes placebetween the rings and the casing, which leakage reduces the efficiencyof the compressor. It has been found that the vanes of a rotor can beproperly supported by a single ring having a width not exceedingfour-tenths of the length of the rotor, and leakages between the cellsformed by the vanes of each cylinder are thus materially reduced.

Other means, and suitable methods of construction described hereinafter,are also utilized to aid in substantially preventing gas leakages frompoints of higher pressure to points of lower pressure, which tend tooccur at different points of the compressor.

Multistage compressors of the sliding vane type, and more particularlycompressors of the two-stage type, usually comprise a plurality ofindependent coaxially arranged cylinders each containing a rotorprovided with vanes, the shafts of the rotors being provided withsuitable couplings connecting such shafts and connecting the shafts witha suitable driving means such as a motor or,prime mover. The cylindersusually rest on a common base, which may enclose or may form aninterstage reservoir or a cooler. Such arrangement, however, results inan instaL- lation of considerable weight, requiring a considerableamount of floor space and necessitating complicated piping between thestages of the compressor and the intercooler and for cooling purposes,such piping being arranged externally of the compressor and its base andrequiring an undesirably large number of pipe joints. Such compressoralso requires stuffing boxes at each point of issue of the shafts fromthe cylinders so that it becomes difficult to maintain the unitssufficiently gas tight. If the intercooler is utilized as a base for thecylinders, such intercooler must be made excessively heavy and is notconveniently accessible for cleaning and repair. The above reciteddisadvantages are all obviated by the use of a compressor comprising aunitary casing forming two coaxial cylinders and an intercooler arrangedabove the cylinders and directly within the casing itself.

It is, accordingly, one of the objects of the present invention toprovide a compressor of the sliding vane type in which the danger of gasleakage from the compressor and between the several cells formed by thevanes, is reduced to a minimum.

Another object of the present invention is to provide a compressor ofthe sliding vane type in which all parts are provided with adequatelubrication for preventing wear between relatively movable parts and forsubstantially preventing leakage of gas from points of higher to pointsof lower pressure within the compressor.

Another object of the present invention is to provide a compressor ofthe multistage sliding vane type comprising a unitary casing for theseveral cylinders.

Another object of the present invention is to provide a compressor ofthe two-stage sliding vane type comprising a unitary casing enclosing aninterstage reservoir or intercooler.

Another object of the present invention is to provide a compressor ofthe multistage sliding vane type requiring only a single stufling boxfor sealing the extension of the shaft from the casing.

Objects and advantages other than those above set forth will be apparentfrom the following description when read in connection with theaccompanying drawing, in which:

Fig. 1 is an axial, vertical, cross-section through a multistagecompressor having a unitary casing enclosing and forming a portion of anintercooler;

Fig. 2 is a transverse cross-section taken along a plane on the line11-11 in Fig. 1;

Fig. 3 is an enlarged fragmentary cross-section taken along a plane onthe line HIIII in Fig. 1;

Fig. 4 is a view of a low pressure rotor vane for a compressor utilizedfor compressing ga. above atmospheric pressure, in which the curvatureof the outer edge of the vane was accentuated;

Fig. 5 is a view of a low pressure rotor vane for a compressor utilizedas a vacuum pump, in which the curvature of the outer edge of the vanewas accentuated.

Fig. 6 is an enlarged portion taken on a plane parallel to the axis ofthe compressor and accentuating the clearances between the wall of oneof the cylinders and the associated floating ring and rotor vanes; and

Fig. '7 is an enlarged portion taken on a plane parallel to the axis ofthe compressor and accentuating the clearances between the wall of oneof the cylinders and the associated floating ring, and showing amodified form of locking ring construction.

Referring more particularly to the drawing by characters of reference,reference numeral ll designates a unitary casing which may be cast ofsuitable material, such as cast iron, or which may be fabricated fromlaminated material to define a pair of adjacent coaxial cylinders If andI3 separated by a partition ll which is provided with passages for theflow of a cooling medium therethrough. Casing II is shaped to form aninlet passage II and an outlet passage 11 for cylinder l2, which is thelow pressure cylinder of the compressor, the casing also forming aninlet passage II and an outlet passage II for cylinder ll,- which is thehigh pressure cylinder of the compressor. The casing further defines orencloses an interstage reservoir or intercooler 2| joining outletpassage I! with inlet passage il, reservoir 2i and the passages having acommon wall provided with ports 22 and 23 providing for directcommunication between the reservoir and passages l1 and II. Thereservoir is arranged above the cylinders and is closed by means of acover 24. All of the connections between the several cylinders and thereservoir are thus arranged internally of the casing and are thusminimized to as great degree as is possible. Reservoir 2| is providedwith cooling means to thereby constitute an intercooler, and thecylinders and the intercooler may be arranged to be cooled by aircirculating thereabout by convection or by forced draft. It is howeverpreferred to shape casing II to form a water jacket surrounding thecylinders and the intercooler, such jacket being provided with a cover21 to give access to the intercooler cover 24. The intercooler thencontains a cooling coil 2. preferably provided with a water inletseparate from the inlet of water jacket 20 and with an outletdischarging into the water jacket thus placing the cooler and Jacket inseries and avoiding failure to cool any part and providing bettertemperature conditionsin the compressors. Coil 20 may be of any of thetypes known in the art, but a coil made of copper tubing provided withfins is to be preferred as a coil of such type requires the least amountof space for a given rate of heat transfer. The air or other gaspropelled by the compressor through the intercooler is preferably causedto follow a sinuous path within the intercooler by means of baffles soas to permit a compact arrangement of the cooling coil. The cooling coilis connected with the inlet and with the outlet thereof by means ofunions, so that the coil may be easily removed from the intercooler forcleaning or for replacement.

It must be noted that the dimensions of both the inlet and dischargeports into the several cylinders is highly important, that is, the ratioof the width of the ports to the length of the cylinder must be keptbetween the values .125 to .162 for cylinder l2 compressing to the lowerpressure and between the values .141 to .147 for cylinder ll compressingto the higher pressure. The above ratios cannot be widely varied withouttoo greatly reducing the internal cylinder surface or too greatlyincreasing the velocity of the air or gas through the ports and theseveral compressor cells which would result in unequal pressures onopposite ends of the vanes or increased air friction losses. Unequalpressures on the vane ends would tend to cause the vanes to rock in therotor slots resulting in uneven wear of the vanes and cylinder walls.

Casing Ii is provided with a pair of cylinder heads ii, 12 preferablyprovided with passages communicating with the water jacket -of thecasing. The cylinder heads are provided with recesses for a plurality ofalined bearings which are arranged eccentricallywith respect tocylinders' l2 and I! for supporting a shaft 38 eccentrically in thecylinders. The bearings are preferably of the antlfriction type and maycomprise a radial bearing 14 arranged in cylinder head 32, a radialbearing arranged in cylinder head 3i, and a thrust bearing 31 actingbetween a shoulder on the shaft 33 and casing Ii through cylinder headIi and through a stuffing box 38. Bearings 36 and 31 may also bereplaced by a combined thrust and radial bearing if so desired. The endof shaft 33 supported in bearing 34 is confined within casing II by abearing cover I bolted on cylinder head 32 and sealed thereagainst, theother end of the shaft being sealed against the casing by a packing 39arranged in stufling box 38. Such packing is the only packing requiredfor the compressor, shaft ll being sealed against partition I by meansof snap rings 43 arranged within grooves of the shaft. The several snaprings are provided with shallow groovesformed radially in the sides onlyof such rings toward the low pressure cylinder 12 to allow sufilcientoil to pass through the grooves with air from the high pressure cylinderto provide for proper lubrication of the rings in the grooves.

Shaft 33 carries a pair of cylindrical rotors, of which the low pressurerotor 44 is mounted on the shaft with a tight fit and is keyed thereon,while the high pressure rotor 06 is splined on the shaft or providedwith a plurality of keys in such manner as to be axially movable withrespect thereto. The ratio of the diameters of the cylinder and therotor should be kept between the values .9 to .904 which determines theratio of eccentricity of the shaft mounting to the diameter of thecylinder which should bekept between the values .05 to .0473. In no caseshould the above values vary greatly from .9 and from .05. The value ofthe first mentioned ratio should be kept as low as possible to maintainvolumetric efllciency and keep the dimensions of the machines as smallas possible but should also be made as large as possible to obtain asufficiently stiff shaft. A very small change in such ratios rapidlyaffects the space available for the shaft within the rotors.

Rotor 44 is provided with a plurality of substantially radial slots eachcontaining a movable blade or vane 41, the vanes being made of heattreated steel, aluminum, artificial resins, fiber composition or othersuitable material, the choice of the material depending upon the speedof shaft 33 and on the conditions of pressure and temperature andcomposition of the gas to be propelled through the compressor. Rotor isalso provided with slots containing a plurality of movable vanes 48. Theuse of artificial resin, fiber composition or similar material for thevanes has been found to be very advantageous for the reason thatadequate lubrication and sealing can then be obtained with the use ofwater soluble oil such as the coolant oils used for metal cuttingpurposes. Such oils are ideal lubricants for the above type of vanes,may be used in very large quantities to secure the most effectivesealing and cooling and are readily separable from air thus allowingdelivery ofoil free air. A reduction in the moisture content of thedelivered air as well as in the degree of corrosion of the compressorare also obtained with the use of such oils.

Cylinder I2 is formed to present a single annular groove in the interiorsurface and having the center thereof at or near the center of thecylinder and containing a single floating ring 49. Ring 49 cannotconveniently be made of segments, and it is accordingly necessary tobore casing II to form a stepped cylinder fully opened at the endthereof adjacent cylinder head 3|, an end ring 5| being fitted at suchend of the cylinder into the step of largest diameter and cooperatingwith the other steps thereof to define a cylinder of uniform diameterhaving a single annular groove substantially equidistant from the endsthereof. Cylinder I3 is similarly provided with a single fioating ring52 arranged in a groove formed by casing H and an end ring 53. As shownin Figs. 1 and 3, ring 49 is preferably made of rectangular crosssectionsubstantially completely filling the complementary groove. The peripheryof the ring is generally cylindrical but so shaped as to form, with thebottom of the groove, a plurality of sector shaped chambers, wherebylubricating oil is forced between the ring and the bottom wall of thegroove during rotation of the ring. The ring is provided with aplurality of radial passages distributed along the periphery thereof toequalize the pressures exerted on the inner and outer peripheriesthereof. Rings 52 and 53 may be similar as shown in Fig. l or may beprovided with a reduced projecting portion 55 and fitting into a singlestep in the cylinder to provide a groove formed by the complementaryaction of the cylinder II and the retaining ring 53, 55 as shown in Fig.7. Such structure of theJetaining rings allows the cylinders l2 and I3to be made with only a single diameter step rather than with twodiameter steps as shown in Fig. l.

A plurality of oil ducts 54 are provided in casing I l for introducinglubricating oil under pressure at the bottom of the cylinder grooves andbetween the end surfaces of the rotors and the complementary surfaces ofthe cylinders, the oil being supplied by any suitable oil pump (notshown). It will be observed that the oil ducts 54 formed in the endheads 3| and 32 extend only to a point adjacent the periphery of therotors 44 and 46 respectively to discharge the oil flowing through suchducts into the clearance space between the end heads and the rotorsclosely adjacent to the periphery'of such rotors. Such locations of theducts is necessary to provide for proper lubrication of the rotor endsand sealing of the clearance spaces due to the tendency of the airpressure to force the oil toward the shaft thus leaving the peripheraledges of the rotors unlubricated and unsealed.

The construction of the compressor will be examined more in detail inconnection with the conditions of pressure and temperature prevailing inthe compressor during operation thereof. During such operation, rotors44 and 46 rotate at a speed such that vanes 41 and 48 are urged againstthe walls of the associated cylinders by centrifugal force. The rotorsbeing eccentrically supported within the cylinders, the vanes thereofcooperate with the cylinder walls in defining cells of variable volumecarrying air or any other gas from one pressure to a higher pressure ifthe machine is used as a compressor or as a vacuum pump, the gas passingfrom one pressure to a lower pressure if the machine is utilized as amotor.

Assuming the machine to operate as an' air or gas compressor, shaft 33being driven by a suitable motor (not shown), air or gas is draw: atsubstantially atmospheric pressure through in let passage l6 intocylinder l2 and is deliverei from cylinder I2 at a higher pressure intopassag II. The air passes through port 22 into inter cooler 2| andthrough port 23 into inlet passag I8 from which it is drawn throughcylinder l3 am delivered into outlet passage [9 and through th' outletport-of the compressor, into a suitable com pressed air delivery system(not shown).

The air compressing operation causes the evo lution of a considerableamount of heat in th' air, such heat being transmitted to the walls 01the casing. and through coil 28 to the water cir culating through thewater jacket and througl the coils. While the walls of the cylinders anmaintained at a relatively low and substantial]: uniform temperature bythe water jacket, thr moving parts of the compressor are subjecte( torelatively high and non-uniform temperatures In particular, consideringthe operation of cylinder l2, ring 49 reaches a temperature which imaterially greater than the. temperature of cas ing II. The ringaccordingly increases in inne: and outer diameters by thermal expansionwhili the cylinder retains substantially its initial diam eter. Undersuch conditions, ring 49 must hav' an inner radius such that vanes 41apply them selves thereagainst and are supported thereby on offrictional engagement with the cylinder wal to thereby avoid wear whichwould result from such frictional engagement. These vanes ar then sealedagainst the cylinder by a film of lubri eating oil. The inner radius ofring 49 mus thus be smaller than the radius of the cylinde bysubstantially the thickness of the oil film t be maintained between thevanes and the cylin der, such radii being measured at the respectivoperating temperatures of the ring and of th cylinder. When thecompressor is being started all parts thereof being at the sametemperature ring 49 is slightly too small in inner diameter so that theclearance between the vanes and th cylinder is slightly too large. Thelubricatin. oil present on the wall of the cylinder has ther however, ahigher viscosity than when such 01 has reached normal runningtemperature, s that an oil film having a thickness equal to th actualclearance of the vanes may be maintainer on the cylinder wall.

To avoid the occurrence of wear between th vanes and the ring, such ringmust be easil' driven by the vanes by frictional engagemen therewith tocause the ring to rotate at substan tially the average speed of theouter edges of th vanes, such edges having only a very slight com binedsliding andoscillating movement with re spect to the ring. To insuresuch operation th outer radius of the ring must be less than th radiusof the complementary groove by the thick ness of a substantial oil film,the maintenance 0 such film being insured by the presence of th sectorshaped chambers defined by the ring an the bottom wall of the groove. Across-sectio; taken through the cylinder and the ring Whel such elementsare at room temperature then ha the appearance indicated in Fig. 3, inwhich radia clearances are, however, accentuated to clarif the drawing.It will be understood that the inne surface of ring 49 is subjected todifferent pres sures at different points thereof due to difl'erendegrees of air compression in the several cell: and that .a side thrusttends to be exerted on th whole ring as a result of the unbalance ofsuc] pressures. Such thrust is avoided by the provision of the radialpassages through the ring whereby the pressures exerted outwardly atevery point of the inner surface of the ring are also exerted inwardlyon corresponding points of the outer surface, the inward and outwardpressures thus balancin! each other.

The width of ring 49 necessary for providing adequate support forvanes41 is determined by the length of the vanes, but must always be madeless than four-tenths of the length of the cylinder I3. The dimensionsof ring 52 are determined by the same considerations as those of ring49. In order to provide sufllcient room beside ring 52 for the portsjoining cylinder II with passages l8 and IS, it is generally necessaryto reduce the width of ring 52, such width however, being not less thantwo-tenths of the length of cylinder IS. The above ratios of floatingring width to cylinder length is highly important because the singlefloating ring must be sufllciently wide to balance the vanes withoutpermitting rocking thereof in the rotor slots in an axial plane. Thesingle floating ring used must be placed substantially centrally in thecylinder and cannot be made so wide as to encroach on the space requiredbetween the cylinder port edges and the edge of the floating ringgroove.

During operation of the compressor, shaft 33 reaches a temperaturehigher than that of casing II, and the shaft accordingly expands axiallyto, a material'extent. The end of shaft 33 adjacent cylinder l2 andcarrying thrust bearing 31 remains in fixed relation to casing I I andthe end surface of rotor 44 adjacent bearing 31 is not materiallydisplaced with respect to the casing upon heating of the shaft. Rotor 44however also expands axially and is accordingly made shorter thancylinder I! by an amount such that the clearance between the rotor andthe partition l4 remains within the range of values suitable for theestablishment of an oil film therein at all operating temperatures. Theend of shaft 33 carrying rotor 46, being remote from thrust bearing 31,is displaced axially to a material extent by thermal expansion of theshaft and it is therefore necessary to leave rotor 46 axially movablewith respect to the shaft. Rotor 46 is made shorter than cylinder II byan amount such that the clearances between the end surfaces of the rotorand of the cylinder are always within the range of values suitable forthe establishment of an oil fllm therein. Such oil films are the solemeans utilized for centering rotor 46 axially in cylinder l3, suchresult being produced by the slight thrust exerted by the oil films onthe end surfaces of the rotor by capillarity. Satisfactory oil films arenot however obtainable unless the oil is supplied at points closelyadjacent to the periphery of the rotor.

The two oil films established on the surfaces of partition l4 by theintroduction of oil through 011 ducts 54 are jointly subjected to thedifference of the pressures exerted by the air in cylinder l2 and incylinder l3. Under the action of such pressure difference, oil tends toflow from cylinder i3 through the bore of partition I4 into cylinder l2and, if the oil films do not extend over the entire surfaces ofpartition l4, air may also leak between the two cylinders through thebore of the partition. Snap rings 43 cooperate with the bore of thepartition in forming a seal of the labyrinth type, such sealsubstantially preventing the flow of oil and of air between'thecylinders under the action of the air pressure.

An absolutely complete prevention of such flow would not materiallyimprove the operation of the compressor and would require the use of apacking, which could be installed and maintained only with considerabledifflculty.

The slight fiow of oil and air within the clearance between rotor 46 andpartition i4 tends to cause the end surface of the rotor adjacent thepartition to be subject to pressures diflering from the pressuresexerted by the oil against the other end surface of the rotor which isnot subject to such oil flow. To obtain an accurate axial centering ofrotor 46 within cylinder ll, it is necessary that the pressures exertedby the oil films on the two end surfaces thereof be substantiallybalanced. Such result is obtained by providing grooves 56 in theperiphery of shaft 13 or in the rotor whereby the two end clearances ofrotor 46 are put in direct communication and are therefore maintained atthe same pressure.

During operation of the compressor, the rotor and the vanes thereof,which are not directly water cooled, are unable to transfer anappreciable amount of heat from the air passing through the compressorto the water jacket. The rotor and the vanes of each stage accordinglyassume temperatures intermediate between the inlet and outlettemperatures of the air passing through such stage. In general, theinner edge of each vane, which isdeeply embedded in the associatedrotor, is at substantially rotor temperature while the outer edge of thevane, whim generally protrudes from the rotor, assumes anothertemperature. As a result of such non-uniformity of temperature, the twoedges of each vane expand by different amounts, thus causing the vane toassume the shape of a fragment of an annulus with the result that theouter edges of the vanes become curvilinear and no longer present auniform clearance with the wall of the cooperating cylinder. Thecurvature of the outer edges of the vanes is usually material only inthe long low pressure vanes,'such as vanes 41, and may becomesufficiently pronounced to render it necessary to make such edgescurvilinear when the vanes are of uniform temperature so that such edgesmay become rectilinear by thermal expansion of the vanes at thenon-uniform operating temperatures thereof.

When the compressor is utilized for compressing air from substantiallyatmospheric pressure to a higher pressure, the outer edges of vanes 41which protrude from rotor 44 mostly on the inlet side of cylinder II,are cooled by the air to a temperature lower than the temperature ofrotor 44, with the result that the distortion of vanes 41 causes theouter edges thereof to become concave. Such occurrence may be preventedby making such edges convex as shown in Fig. 4, the convexity of theedgewhen the vane is at uniform temperature being such that the edgebecomes substantially rectilinear at the non-uniform operatingtemperature of the vane.

when the compressor is utilized as a vacuum pump to compress gas from apressure materially below atmospheric pressure to substantiallyatmospheric pressure, the cooling efl'ect of the air in the inletpassage on the outer edge of the vane 41 is negligible, and such outeredges are then heated by the air being compressed in cylinder 12 to atemperature higher than the temperature of rotor 44. Such outer edgesaccordingly tend to become convex and are preferably made concave whenthe vanes are at uniform temperature'so as to become rectilinear whenthe vanes reach the non-uniform operating temperature thereof. Thecurvature of the vanes is always very slight, so that when thecompressor is started and the vanes are at uniform temperature an oilfilm may still be maintained between the outer edges of the vanes andthe wall of the cylinder.

It will be apparent that many of the novel structural features hereindisclosed such as the single floating ring in each cylinder, the mannerof supplying oil to the cylinder end heads, the composition blades andwater soluble oil lubrication, etc. are applicable to both multistageand single stage compressors of the sliding vane type and as sosuitable, have been separately claimed herein.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to those skilled in theart that various changes-and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

1. In a rotary compressor, a casing defining a cylinder having a grooveformed in the inner surface thereof, a rotor eccentrically supported insaid cylinder and having a plurality of slots therein, a plurality ofvanes movably mounted in the slots of said rotor, said vanes being urgedtoward the wall of said cylinder upon rotation of said rotor, and a ringmounted in the groove in said cylinder for supporting said vanes out offrictional engagement with the inner surface of said cylinder, said ringbeing provided with apertures therethrough and having the outerperiphery formed with plane surfaces about the apertures to form sectorshaped chambers with the surface of the groove.

2. In a rotary machine of the sliding vane type, a casing defining acylinder, a rotor eccentrically supported in said cylinder and having aplurality of slots therein, and a plurality of vanes of rectangularcross section severally movably mounted in the slots in said rotor, saidvanes being urged toward the wall of said cylinder and beyond theperiphery of said rotor upon rotation thereof, the longitudinal edges ofsaid vanes extending beyond the periphery of said'rotor being madecurvilinear relative to the axis of said vanes by a sufficient amount toprovide a rectilinear edge of said vanes due to thermal expansionthereof during operation of the machine.

3. In a rotary machine of the sliding vane type, a. casing defining acylinder, a rotor eccentrically supported in said cylinder and having aplurality of slots therein, and a plurality of vanes of rectangularcross section severally movably mounted in the slots in said rotor, saidvanes being urged toward the wall of said cylinder and beyond theperiphery of said rotor upon rotation thereof, the edges of said vanesextending beyond the periphery of said rotor being made convex relativeto the axis of said vanes by a suflicicnt amount to provide arectilinear edge of said vanes due to thermal expansion thereof duringoperation of the machine as a compressor.

4. In a rotary machine of the sliding vane type, a casing defining acylinder, a rotor eccentrically supported in said cylinder and having aplurality of slots therein, and a plurality of vanes of rectangularcross section severally movably mounted in the slots in said rotor, saidvanes being urged toward the wall of said cylinder and beyond theperiphery of said rotor upon rotation thereof, the edges of said vanesextending beyond the periphery of said rotor being made concave relativeto the axis of said vanes by a sufiicient amount to provide arectilinear edge of said vanes due to thermal expansion thereof duringoperation of the machine as an exhauster.

5. In a rotary machine of the sliding vane type. a casing defining acylinder formed to provide a single substantially centrally locatedgroove therein, a ring mounted in the groove, a rotor eccentricallysupported in said cylinder and having a plurality of slots therein, anda plurality of vanes of rectangular cross section severally movablymounted in the slots in said rotor, said vanes being urged toward thewall of said cylinder into engagement only with said ring and beyond theperiphery of said rotor upon rotation thereof, the

edges of said vanes being made curvilinear relative to the axis of saidvanes by a sufiicient amount to provide a rectilinear edge of said vanesdue to thermal expansion thereof during operation of the machine.

6. In a rotary machine of the sliding vane type, a casing defining acylinder formed to provide a single substantially centrally locatedgroove therein, a ring mounted in the groove, a rotor eccentricallysupported in said cylinder and having a plurality of slots therein, anda plurality of vanes of rectangular cross section severally move ablymounted in the slots in said rotor, said vanes being urged toward thewall of said cylinder into engagement only with said ring and beyond theperiphery of said rotor upon rotation thereof, the edges of said vanesbeing made convex relative to the axis of said vanes by a sufficientamount to provide a rectilinear edge of said vanes due to thermalexpansion thereof during operation of the machine as a compressor.

7 In a rotary machine of the sliding vane type, a casing defining acylinder formed to provide a single substantially centrally locatedgroove therein, a ring mounted in the groove, a rotor eccentricallysupported in said cylinder and having a plurality of slots therein, anda plurality of vanes of rectangular cross section severally movablymounted in the slots in said rotor, said vanes being urged toward thewall of said cylinder into engagement only with said ring and beyond theperiphery of said rotor upon rotation thereof, the edges of said vanesbeing made concave relative to the axis of said vanes by a sufiicientamount to provide a rectilinear edge of said vanes due to thermalexpansion thereof during operation of the machine as an exhauster.

8. In a rotary compressor of the sliding vane type, a casing defining acylinder having a groove formed in the inner surface thereof and havingports thereinto, a rotor eccentrically supported in said cylinder andhaving a plurality of slots therein, a plurality of vanes slidablymounted in the slots in said rotor, said vanes being urged toward thewall of said cylinder upon rotation of said rotor, and a ring mounted inthe groove in said cylinder for supporting said vanes ,out of frictionalengagement with said cylinder, the width of the ports and of said ringbeing between the limits-of one-sixth and one-eighth and between thelimits of two-tenths and four-tenths, respectively, of the length ofsaid cylinder.

GUSTAF L. KOLLBERG. MELVIN C. SHAW.

